gether beyond the control of the will. Where convulsions arise from sympathy, as in teething, or irritation of the bowels, the painful impression is transmitted to the brain, and hence reflected back upon the muscles. Thus pricking the finger with a needle has thrown a nervous woman into spasms, by exciting the brain to action.

32 If a nerve which supplies any voluntary muscle be divided, that muscle will no longer contract. This proves that the influence of the brain is necessary. In palsy, there is generally some disease of the brain, as the rupture of a small blood-vessel, or tumour growing in its substance. Here the power of the will, or the faculty of volition is not destroyed; but the brain is unable to carry into execution the command of the will, as when a person is very willing to take a load upon his back, but he happens not to have suffi cient strength to carry it.

33. During sleep, all voluntary motion is suspended, be cause the brain ceases to act. In those cases where persons walk and talk in their sleep, the brain is not entirely dormant. Some of the senses seem to be awake at times, while the others are asleep. That is, those portions of the brain which are excited to action by certain nerves of sense, are awake and active, while other portions are dormant and at rest. The brain needs repose and relaxation, as much as the muscles. Periodical cessation of effort is necessary to both, in order to a vigorous performance of their respective functions.

Questions. What functions belong to the nervous system? What does it embrace? How many departments? What offices does each perform? What marks characterize each? When their functions are interrupted, what happens? From what portion of the spinal mar. row do the nerves of motion arise ?-the nerves of sensation? Describe the brain ;-its divisions ;-its membranes ;-dura mater ;-pice mater; What are the convolutions of the brain? How do the cine. ritious and medullary portions differ from each other? Which is ex terior? How many cavities in the brain? What are they called?

Describe the cerebellum,-the spinal marrow. How many pairs of nerves are there? How many nerves arise from the cerebrum ?from the pons varolii from the spinal marrow-from the medulla oblongata? How many principal ganglia or net-works of nerves 1+their situation? What is a ganglion? What are the principal ganglions of the nervous system of organic life? What is the sympathetic nerve ? -where situated? What is the most important organ of the body? What is said of the brain in the lower animals? Over what functions does the brain preside? Is it immaterial What is the first class of functions over which it presides? What is understood by sensorial functions? What becomes of the senses during sleep?-during absentmindedness? What are ideas? Is atte: tion necessary in order to impress sensations durably on the mind? May sensations be excited without the intervention of sensible objects? In what disease does this happen? Is the brain itself sensible? Where is the seat of voluntary motion? How is it performed? What is volition? Are motions always under the control of the will? In what diseases is this not the case? What effect has the division of a nerve? What happens in palsy? Why is voluntary motion suspended during sleep?

CHAPTER X.

INTELLECTUAL AND MORAL FACULTIES.

1. THE great superiority of the intellectual faculties of man over those of other animals, has led to a diligent examination, whether there be any thing in his anatomical structure which would seem to account for this superiority. Aristotle noticed the great size of the human brain compared with that of other animals, and laid it down as a general principle, that the faculties referred to this organ were in proportion to its size, compared with that of the whole body Though this rule will hold true in relation to some of the domestic animals, yet it does not in relation to many others, for accurate researches have shown that while in man the ratio of the weight of the brain to that of the whole body is as 1 to 28 in the dog, it is as 1 to 160, in the horse, as 1 to 400) in the elephant, 1 to 500, in the canary bird, 1 to 14, (and in one species of ape, 1 to 11.)

2. It is now generally admitted by physiologists, that the perfection of the sensitive functions does not depend on the absolute size of the brain, nor on its proportion to the body at large, but upon the proportion between the size of the brain, and the aggregate bulk of the nerves that proceed from it; in other words, between the sensorial and nervous organs For example, the absolute size of the brain of the horse is only about half the size of the human brain, while the mass of the nerves of the horse at their origin is no less than ten times larger than that of man. Extensive observa. tions prove that though most of the inferior animals have larger nerves, and possess some of the nervous functions in a much more acute state than man, yet man decidedly exceeds them all in the comparative size of the brain, and in the perfection of his intellectual faculties.

3. The brain then, is the organ of the intellectual and moral faculties, the material instrument of the mind. This is proved not only by comparative anatomy, and experiments on animals, but by the history of injuries of the brain, compared with those of other organs. We know that if the nerves supplying any limb are severed, the will has no longer any influence over it; it is to all useful purposes a dead por. tion of matter. The same is true of the spinal marrow. If this be compressed by fracture or dislocation of the spine, the whole body below that point, is deprived both of sensation and motion, but the mind loses none of its powers any more than if a limb had been amputated.

4. If the brain is not the seat of the intellectual faculties, neither are any of the other organs of the body. The lungs, the liver, the spleen, the intestines, or the kidneys, may be affected with gangrene, and still the mind remains clear; though from sympathy, inflammation of any organ may cause delirium, or other mental affections. Neither is the heart the seat of the mind; for cronic disease of that organ, does not impair the mental faculties. Besides the functions of all these organs are known and cannot be mistaken. If the brain is not the seat of the intellectual faculties, they cannot be said to have any seat in the body.

5. But the effects of injuries of the brain are very diffe rent, for every cause which disturbs its action suddenly or slowly, affects at the same time the mind. Inflammation of the brain is always attended with delirium, or stupor; pressure on it, whether produced by depressed bone, foreign bodies, a tumour, serum, blood or pus, always gives rise to similar symptoms, and often destroy both sensation and motion. In cases of apoplexy, where a person falls in a fit, and becomes insensible, we find pressure on the brain from effusion of blood or serum. In cases of lunatics, we find in nearly all cronic cases, structural changes in the brain; but if the case be recent, these changes though they probably exist, yet may escape our imperfect means of investigation. Alcohol, opium, and other narcotics affect the mind and the

nerves through their influence upon the brain. Whenever in fact, we see a person become stupid and insensible, we may be certain that the brain has suffered some physical change; and where in cases of sickness, we see the mental faculties unimpaired to the last, we may be equally sure, that the brain is not affected.

6. The following facts also show that the brain is the organ of the mind. A man received a blow on his head, and immediately lost his mental faculties, and his bodily power. His appetite and digestion were good; the blood circulated freely; and his breathing and pulse were natural. He continued in this state more than a year, when a surgeon raised up a piece of bone which had been driven in upon the brain. His reason was immediately restored; the next day he spoke, and in a short time he recovered entirely; but he could recollect nothing of what had happened since the accident. Not long since a beggar exhibited himself in Paris, who had lost a portion of his skull; his brain was only cov. ered by the skin and membranes. For a trifling sum he would allow any one to press on this exposed part. As soon as any pressure was made he became wholly unconscious; but his intellect was immediately restored when the pressure was taken off.

7. (It has been objected to the brain's being considered the seat of the mind, that in some cases, considerable disease has been found affecting an entire hemisphere without the mental faculties having suffered; but experiments on animals show that a sudden lesion of one hemisphere only, does not immediately produce complete stupor, and that this effect does not follow until both are removed; so that it appears that one hemisphere aids the other, and compensates for its inaction in the operations of the mind.

8. But though it is almost universally admitted, that the brain is the seat of the higher intellectual faculties, yet some physiologists, like Bichat, contend that the passions are seated in the thoracic and abdominal viscera. It is, however,